Electronic hearing systems utilizing implanted electrodes to electrically stimulate the auditory nerve are increasingly used to produce the sensation of hearing in the deaf. Examples of such systems are disclosed in U.S. Pat. Nos. 4,419,995 and 4,617,913. The quality of the electrode/tissue connection is of primary importance to the performance of any implanted electrode system. In particular, the quality of the connection directly affects the level of current that can be applied through an electrode, and consequently the quality and intensity of the electrical stimulation delivered to the auditory nerve.
The absolute current density of current flowing through an implanted electrode is an important parameter of its function. If the absolute current density through an electrode is too high, unwanted irreversible reactions can occur. For instance, metals and chemicals from the electrode may be released into the surrounding tissue, or in extreme cases body fluids may be hydrolyzed.
Information on absolute current density is thus of considerable value for the purpose of fitting an implant system to be sure that it is operating within safe limits. Absolute current density also can be used to identify an internal shunt which is disrupting the operation of the electrode, or to measure the stability of an implant system over time. Thus, it would be highly desirable if a simple and practical method for determining absolute current density through an implanted electrode were available.